Although a large amount of information on the structure, function and interaction of myofibrillar proteins is available, very little is known about the biogenesis of the myofilaments and how this process is regulated. One aim of this proposal is to study in detail the regulatory mechanisms involved in the synthesis of the various myofibrillar proteins and how this process is correlated with the assembly of myofilaments during muscle growth. Recent studies in this and other laboratories have suggested that following embryonic development when striated muscles differentiate to the characteristic fiber type (e.g., skeletal slow, fast, cardiac, etc.) they contain different isozymic forms of myofibrillar proteins such as myosin light chains, tropomyosin subunits, etc. which are known to be coded by sets of very similar yet structurally different genes. We now plan to test whether or not this observed polymorphism of myofibrillar proteins in muscle fibers is regulated by cellular and physiological processes such as adaptive response to electrical stimulation and cross reinnervation. Another aim of the proposed studies is to study in detail whether or not translational control is involved in the regulation of myogenesis during growth and differentiation of embryonic muscle cells.